A vacuum cleaner head may include an agitating member, such as a rotatably mounted brush, which is used to agitate the surface over which the vacuum cleaner head travels (e.g. carpet). The agitation of the surface, in conjunction with the air stream entering the vacuum cleaner head via a dirty air inlet, entrains dirt which may be, for example, embedded in a carpet.
It is known to adjust the height of a brush of a vacuum cleaner head so as to more optimally position a brush depending upon the surface which is being cleaned. In particular, it is known in the art to increase the distance of the brush from the carpet being cleaned as the thickness or pile of the carpet increases. For example, U.S. Pat. No. 3,683,448 (Lagerstrom et al) discloses a nozzle height adjustment mechanism for adjusting the height of a suction inlet with respect to the surface being cleaned. Lagerstrom et al uses a rotatably mounted axle and a cam surface which engages a radially off set central portion of the axle. One disadvantage of this approach is that an operator must manually set the height of the inlet based upon the operator's evaluation of the surface being cleaned.
U.S. Pat. No. 5,086,538 (Zahuranec) discloses a foot operated nozzle height adjustment mechanism. U.S. Pat. No. 4,513,472 (Wells) also discloses a height adjustment mechanism which requires initial operation of the device by the user. The operator then turns the vacuum cleaner on and slowly steps on an actuator while the front cleaning nozzle is slowly lowered to the floor. When the proper vacuum is achieved, the nozzle is fixed at a set height (column 4, lines 32-49). Accordingly, Wells et al and Zahuranec disclose height adjustment mechanisms which are manually operable.
U.S. Pat. No. 3,849,823 (Adamson et al) discloses a floor cleaning apparatus which has a rotatably mounted brush. When the brush meets an increased resistance in cleaning the floor covering, the brush is elevated to reduce the resistance to rotation. The mechanical linkage of Adamson et al is used to reduce the load on the turbine so as to enable the brush to keep rotating but does not directly monitor the air flow in the vacuum cleaner.